The late Richard Hardesty was a respected audio engineer, consultant, writer,
reviewer, and -- I read somewhere -- he could play a mean piano. He was also an
early dealer of true high end audio in Southern California. In his early retail days he drove to customers homes armed with
a heavy load of audio test gear to deal with acoustical issues. As time passed the amount of heavy gear
decreased as most succeeding visits became a near
acoustical
replay of previous visits. Although his test gear must have
looked cool in his customer's eyes, much of the heavy gear was seldom needed. It had become apparent that, acoustically, most rooms were just another enclosed box with predictable issues and routine solutions. The goal of this chapter
is to skip the heavy gear
phase altogether and still solve acoustical issues with a practical mix of advice from Mr. Hardesty, the
'Master Handbook
of Acoustics', Auralex Acoustics, long forgotten sources, plus many of my colleagues --- in
particular my late friend Steve Mounkes.

The acoustical smallroom ...... is your room

As outlined in Chapter 2, the compressions and rarefactions of sound waves are described by their wavelength, amplitude, and frequency. The frequency of audible sound ranges from 20Hz to 20KHz with wavelengths from 56.5 ft to about 3/4 of an inch. The acoustical small is any room with dimensions that are comparable to acoustical wavelengths. Therefore, any room with a dimension of 56.5 feet or less qualifies as an acoustical small room (this includes ceiling height). This acoustical small room is an environment that can erupt into a resonating
cavity of
agitated low frequency
energy(300Hz & below). This room can also act as an acoustical reflecting mirror
of higher frequency sound that
competes with the direct sound from the speaker system. It may even have a noisy neighbor. The acoustical small room is your room and it has a predisposition to generate acoustical
distortion.

Acoustical distortion Audio distortion
is the corruption of sound. Acoustical distortion is audio distortion created
by the room environment. Three types of acoustical perception are
affected by acoustical distortion: timber, imaging,
and spatial impression. Acoustical distortion is influenced by
room modes, specular reflections, comb filtering, absorption,
diffusion, and noise. In the acoustical small room the management
of room modes, specular reflections, and noise are the principal
concern.

Handbook
Note:Speed
of sound = 1130ft/sec.

Room modes
Each
boundary of the acoustical small room causes sound energy to
resonate much as waves in the ocean. This resonating
sound is defined as standing waves or room modes. Primary axial
room modes
of opposite boundaries (length, width, & height) are the most
significant. They can
produce an uneven distribution of low frequency sound that causes
deviations from flat frequencyresponse. That is a
principle definition of distortion.
The wavelengths of the 3 primary axial modes are equal todividing half the
speed of sound by its room dimension -- length,
width, height.

Specular reflections Specular reflections are
room boundary reflections of short acoustical wavelength that compete
with the direct sound from a speaker. They distort imaging and spatial
impression. Their physics is identical to a ray of light reflecting
off a mirror. Formally this is defined as "the angle of incidence
equals the angle of reflection".

Noise
Noise is random unwanted competing
sound. It is the most corruptive acoustical distortion. As specular reflections -- noise generated from within the room or an adjoining area distorts imaging and the spatial impression of sound fields. Noise also erases musical
harmonic detail, skews timbre, and reduces dynamic range. Noise distorts audio. 1- 2 - 3 - 4 > next

Ed's
AV Handbook.com Batting
Practice for the AV Pro and a Primer for the Novice.Copyright
2007 Txu1-598-288 Revised 2018